分治回溯-----回溯的問題之數獨問題

package 分治回溯;

import java.util.Scanner;

public class Sudcku {
    public static void main(String[] args) {
        int [][] board=new int[9][9];
        Scanner scanner=new Scanner(System.in);
        //"005300000"
        for (int i=0;i<board.length;i++){
            String line=scanner.nextLine();
            for (int j=0;j<board.length;j++){
                board[i][j]=Integer.parseInt(line.charAt(j)+"");
            }
        }
        solve(0,0,board);
    }

    private static void solve(int row, int col, int[][] board) {
        if (row==9){
            print(board);
            return;
        }else {
            if (board[row][col]==0){
                for (int num=1;num<=9;num++){
                    if (!isExist(row,col,num,board)){
                        board[row][col]=num;
                        solve(row+(col+1)/9,(col+1)%9,board);
                    }
                    board[row][col]=0;
                }
            }else {
                solve(row+(col+1)/9,(col+1)%9,board);
            }
        }
    }

    private static boolean isExist(int row, int col, int num, int[][] board) {
        //同行
        for (int c=0;c<9;c++){
            if (board[row][c]==num){
                return true;
            }
        }
        //同列
        for (int r=0;r<9;r++){
             if (board[r][col]==num){
                 return true;
             }
        }
        //3*3
        int rowMin=0;
        int colMin=0;
        int rowMax=0;
        int colMax=0;
        if (row>=0&&row<=2){
            rowMin=0;
            rowMax=2;
        }
        if (row>=3&&row<=5){
            rowMin=3;
            rowMax=5;
        }
        if (row>=6&&row<=8){
            rowMin=6;
            rowMax=8;
        }
        if (col>=0&&col<=2){
            colMin=0;
            colMax=2;
        }
        if (col>=3&&col<=5){
            colMin=3;
            colMax=5;
        }
        if (col>=6&&col<=8){
            colMin=6;
            colMax=8;
        }

        for (int r=rowMin;r<=rowMax;r++){
            for (int c=colMin;c<=colMax;c++){
                if (board[r][c]==num){
                    return true;
                }
            }
        }
        return false;
    }

    private static void print(int[][] board) {
        for (int i=0;i<board.length;i++){
            for (int j=0;j<board.length;j++){
                System.out.print(board[i][j]+" ");
            }
            System.out.println();
        }
    }
}